Research findings on the potential causal association between adolescent risk taking (substance use and sexual risk) and depression are mixed. Some studies suggest risk behavior leads to depression while others suggest depression increases risk behavior.1-5 A Stress Model suggests risk behavior leads to depression by inciting the body's stress response, an endocrine reaction to novelty exposure, which subsequently increases inflammation and risk of depressive symptoms.6-10 An alternative Self-Medication Model suggests depressed adolescents may use substances or engage in sexual risk taking to self-medicate their depression.1 In the latter model, depression decreases impulse control and modifies psychosocial functioning (e.g., reduces motivation).5,11 Biological sex further complicates these issues; females are less likely to engage in risk behavior but have higher rates of depression, whereas males take more risks but have lower rates of depression.1,2,12,13 It is not clear whether or how the developmental processes linking risk behavior and depression vary by sex, however. In addition to health risk during adolescence, these associations may have long-term implications for health, including substance dependency and establishment of pre-disease pathways, as both depression and stress can increase inflammation, and when chronic, harm immune function.14-17 This project will use data from the National Longitudinal Study of Adolescent Health (Add Health) to address two research aims: 1) examine, separately for males and females, time lagged associations between risk taking (substance use/sexual risk) and depressive symptoms to assess directionality; 2) identify risk taking/depressive symptom profiles across adolescence and emerging adulthood, and group adolescents with similar profiles into latent classes; 3) examine the potential young adult health implications (e.g., substance abuse/dependency, sexually transmitted infections (STIs), pre-disease pathways) of latent class membership (i.e., patterns of risk over time) using both self-report and biomarker data. Add Health data allow for prospective examination of sex differences in these associations from adolescence into young adulthood in a large, racially diverse, national sample. Analytical methods will include repeated measures and mixed regression models to look at associations between depressive symptoms and risk taking over time, Latent Class Growth Models to group individuals' risk taking and depressive symptom trajectories by type, and appropriate regression methods to link class membership to health outcomes in young adulthood. Findings will enhance our understanding of the immediate and long-term health implications of patterns of adolescent risk taking, and inform intervention efforts.